Influence of Matrix and Surfactant on Piezoelectric and Dielectric Properties of Screen-Printed BaTiO3/PVDF Composites.

The aim of this paper was to provide insight into the impact of matrix and surfactants on the rheology, morphology, and dielectric and piezoelectric properties of screen-printed BaTiO3/PVDF composites. Two matrices were compared (PVDF-HFP and PVDF-TrFE), and lead-free BaTiO3 microparticles were added in volume fractions of 30% and 60%. Here, we demonstrated that the presence of surfactants, helping to prevent phase separation, was crucial for achieving a decent screen-printing process. Fourier-transform infrared (FTIR) spectroscopy together with scanning electron microscopy (SEM) showed that the two "fluoro-benzoic acid" surfactants established stable bonds with BaTiO3 and improved the dispersion homogeneity, while the "fluoro-silane" proved to be ineffective due to it evaporating during the functionalization process. PVDF-TrFE composites featured a more homogeneous composite layer, with fewer flaws and lower roughness, as compared with PVDF-HFP composites, and their inks were characterized by a higher viscosity. The samples were polarized in either AC or DC mode, at two different temperatures (25 °C and 80 °C). The 30% BaTiO3 PVDF-TrFE composites with two fluorinated surfactants featured a higher value of permittivity. The choice of the surfactant did not affect the permittivity of the PVDF-HFP composites. Concerning the d33 piezoelectric coefficient, experimental results pointed out that PVDF-TrFE matrices made it possible to obtain higher values, and that the best results were achieved in the absence of surfactants (or by employing the fluoro-silane). For instance, in the composites with 60% BaTiO3 and polarized at 80 °C, a d33 of 7-8 pC/N was measured, which is higher than the values reported in the literature.